Antibodies raised against a glucose-containing tetrasaccharide- GlcAlpha1-6GlcAlpha1-4GlcAlpha1-4Glc-coupled to KLH have been used in a radioimmunoassay to measure urinary excretion of the oligosaccharide in urine of patients with glycogenoses, pregnant women, and pediatric patients with soft tissue sarcomas. Preliminary data suggest that the rate of urinary excretion of this tetrasaccharide may be a useful indicator of the tumor mass present in certain patients. The oligosaccharide has been shown to originate from glycogen as a limit dextrin produced by the combined actions of alpha amylase and neutral alpha glycosidase in plasma.